Size Classes, Reproductive Behavior, and Insect Associates of Cycas media (Cycadaceae) in Australia

A survey of Cycas media in northern Queensland, Australia, showed no differences between males and females in leaf number and stem height. Leaf numbers and stem heights were normally distributed in all populations sampled. The mass of fresh nearly mature seeds from individual females was about three times greater than the mass of the single fresh cone produced by individual males, suggesting that resource allocation to reproduction is greater for females than for males. The proportions of putatively mature individuals participating in the two reproductive episodes evident during the study were between 14% and 38%. On an overall population basis, including immature plants or those otherwise too small to produce cones, the proportion of individuals without reproductive structures ranged from 56% to 93%. Leaf life is of short duration and many naturally defoliated plants were present. Leaf production appears to be stimulated by fire, estimated to occur every 2 or 3 yr. Species belonging to two genera of Coleoptera were collected from male cones shedding pollen, and individuals of the bee Trigona carbonaria were observed collecting pollen from these cones. The genus Trigona is the oldest known fossil bee; it seems possible that it may have collected gymnosperm pollen prior to the origin of angiosperms and that this association has persisted to the present.